For Hodgkin lymphoma (HL), a common cancer of children and young adults, epidemiologic research has identified some risk factors, but the most important finding has been significant heterogeneity across patient and tumor characteristics (e.g., age, histologic subtype, tumor cell Epstein-Barr virus). Thus, the etiology of HL remains unclear, and in large part this is because its low incidence limits study sample sizes, particularly for the stratified analyses required addressing this heterogeneity. For the ultimate aim of primary prevention, additional studies of HL risk factors therefore are needed, but they must be very large. With the very efficient approach of combining existing HL epidemiologic data resources for collaborative re-analyses, we propose to form a consortium of HL studies within the NCI Inter Lymph consortium, pool data from these studies, and use the pooled dataset initially to test two novel hypotheses not addressable in individual studies. The study aims are to: 1) obtain and summarize descriptive information (data dictionaries, questionnaires, lists of data resources), and core demographic and tumor data for future analysis planning, from all participating HL studies;2) post summarized study information and pooled core data frequencies on the Inter Lymph internet portal for reference for planning future analysis;3) in the pooled dataset, test whether: a) ultraviolet light exposure is inversely related to HL risk;and b) HL cases with and without a family history of HL or lymphoma have differing risk factors suggesting environmental modification of genetic susceptibility. Leaders of 22 international HL studies have agreed to pool their resources (interview data, tumor specimens, and/or DNA on ~16,000 HL cases and 37,000 controls), following well-established and successful Inter Lymph policies and procedures. The pooled resource will be among the largest databases for study HL etiology ever compiled. Study strengths include: 1) producing a very powerful database for evaluating novel and extant risk factors within and across etiologically relevant subcategories of HL, for a level of insight about HL causes and outcomes not heretofore possible;2) extremely efficient use of existing resources, with a large information gain for a relatively small cost;3) efficient use of existing infrastructure in a successful international consortium of epidemiologic studies;4) initial analyses in the pooled data in two promising areas: ultraviolet light exposure, a novel HL risk factor that is modifiable;and environmental modification of the well-described familial HL, with implications for etiology and clinical management of high-risk families.